Patients undergoing major surgery, for example, open heart surgery, typically have the functions of the heart and the lungs temporarily performed by various apparata in an external (extracorporeal) circuit. These functions may be performed by the apparatus rather than the heart and lungs of the patient since the patient's heart may be temporarily prevented from contracting or beating during the surgery. The contractions of the patient's heart may be stopped or arrested by a technique known as cardioplegia, which involves using chemical compounds, and/or cold, to arrest the contractions of the cardiac muscle, known as the myocardium.
During a typical operation requiring extracorporeal circulation, whole blood from the cardiovascular system of the patient is typically taken from the patient and collected in a container such as a venous reservoir. A wide variety of diluents, such as plasma, saline, heparin, and the like may be added to the whole blood. A pump is used to withdraw the blood from the venous reservoir and then deliver it to a gas exchanger, such as an oxygenator, which serves as an external lung. The gas exchanger may be combined with a heat exchanger to also control the temperature of the blood. Within the gas exchanger, blood is exposed to an appropriate percentage of oxygen. The exchanger may have more than one outlet, such that blood may be passed through one outlet of the exchanger and delivered to a blood filter, which removes gaseous microemboli, fat emboli, aggregates and microaggregates, and other debris. From the filter, the blood is usually returned via the arterial line directly to the vascular system of the patient.
Blood may also be passed through another outlet of the exchanger, through a different flow path involving the cardioplegia circuit. Blood passing through the cardioplegia circuit is combined with a cardioplegia fluid, such as a fluid including a high concentration of potassium. This mixture of cardioplegia fluid and blood is typically passed through a heat exchanger to cool the mixture, and then delivered to the heart, to arrest the contractions of the myocardium. After the surgery is completed, blood may be mixed with a cardioplegia fluid of lesser potassium concentration, this mixture may be warmed by passage through the heat exchanger, and the warmed mixture may be delivered to the heart before normal contractions are reinstituted.
Ancillary circuits, typically including at least one additional pump and an additional container, may be used to collect and possibly filter the blood accumulating at the operative site or elsewhere. The collected blood is delivered to the additional container, the cardiotomy reservoir, where it can be stored until the surgeon returns the blood to the patient's cardiovascular system. For example, the blood may be directed from the cardiotomy reservoir to the venous reservoir, and returned via the arterial line as described previously. By these means, the collected blood is salvaged and the need for supplemental blood replacement may be minimized.
Technological improvements involving extracorporeal circuits have generally focused on, for example, minimizing red cell damage in the arterial and cardiotomy filters, and improving the collection and salvaging efficiency of the circuits including these filters. Furthermore, since these devices are foreign to the patient's body, and may have a deleterious effect on leukocytes in the blood, some arterial filters may be designed to provide for leukocyte depletion as the blood passes repeatedly through the device. For example, during a typical operation involving a cardiac bypass, the leukocyte removal filters used in the arterial line circuit may be generally capable of removing a portion of the leukocytes in the blood recirculating in the circuit.
Leukocyte depletion may be desirable since contact between the internal surfaces of these foreign devices and the leukocytes may activate the leukocytes. This is turn may elicit an immune response and/or may result in the formation and release of a host of toxic mediators, and what is commonly referred to as oxygen-free radicals. If the leukocytes have been activated, but lack an appropriate antigenic target, the leukocytes may inflict damage to internal organs, particularly those tissues in which no blood is flowing such as the heart and lungs during certain surgical procedures.
However, none of the technological improvements noted above have addressed the need to remove deleterious matter, especially leukocytes, from fluids in a cardioplegia circuit, e.g., blood or cardioplegia fluid mixed with blood. Such removal would be especially desirable, since cardioplegia fluids and mixtures, unlike the blood returned to the body via the arterial line, are typically delivered directly to the heart. Cardioplegia fluids and mixtures are typically not a part of a recirculating system, and as a result, there is essentially only one chance to remove deleterious matter such as fat emboli, aggregates, microaggregates, leukocytes and debris from the fluid before it reaches the heart. The failure to remove deleterious matter from cardioplegia fluids and mixtures may result in "embarrassing" or "shocking" the heart by exposing it directly to this deleterious matter. Moreover, exposure to the most common leukocyte, the granulocytic neutrophil, is undesirable, since this leukocyte has been implicated as the mediator of tissue destructive events in a variety of disorders, including reperfusion injury. The commonality which pervades these pathologies is the neutrophil's ability to release a number of agents which can disrupt and destroy normal cellular function, dissolve connective tissue, and cause injury to organs. Accordingly, it would be desirable to provide a process, device and system for removing or depleting deleterious matter from cardioplegia fluids and mixtures to minimize the exposure of the heart to such matter.
These and other advantages of the present invention will be apparent from the description as set forth below.